Due to various factors, such as the accuracy, repeatability, and resolution of a robot arm, interference and collisions usually occur between a workpiece and its designated location while using the robot arm in insertion and mating maneuvers and thus result in unexpected orientational and angular errors. Passive remote center compliance (RCC) devices are one of commonly used techniques for attending such problems and for enhancing the dexterity of the robot arm.
A remote center compliance device is a passive device for aiding insertion and mating maneuvers in robot machines, docking, and assembly equipment. An RCC device establishes motion about a remote center typically at, near or beyond the functioning end of the operator member. The RCC device usually includes two structures concatenated or serially interconnected between an operator member and a mounting member.
In one type of RCC device, as disclosed in U.S. Pat. No. 4,098,001, an RCC device includes flexure means comprised of a number of discrete elements aligned with radii from a center which is the remote center of the device. Such an RCC device comprises flexures arranged in parallel configuration (56, 68, 60), flexures arranged in trapezoidal configuration (24, 26, 28), and segments, wherein the flexures arranged in parallel configuration (56, 58, 60) establish motion, the flexures arranged in trapezoidal configuration (24, 26, 28) establish angular motion, and the segments are connected by reduced portions (30, 32, 34, 36, 40). Therefore, the rising angle of such an RCC device is usually less than 1.5.degree.. The motion transfer is established by the net force and net torque encountered at the remote compliance center, wherein the net force enables translational compliance at the flexures arranged in parallel configuration, and the net torque enables angular compliance at the flexures arranged in trapezoidal configuration.
Other known RCC devices include U.S. Pat. No. 4,355,469 which provides an improved RCC device with enlarged error tolerance, U.S. Pat. No. 4,477,975 which provides an improved, adjustable RCC device having an easily and quickly adjusted remote center of compliance, U.S. Pat. No. 4,556,203 which provides an RCC device with improved linearity and uniformity of its compliant response, and U.S. Pat. No. 4,848,757 which provides an improved RCC device utilizing partially coil-bound springs as compliant elements.
However, since the structures of these disclosed RCC devices all fail to provide rotational degree of freedom in orientation, they are merely adapted to insertion and mating maneuvers of round pegs. Furthermore, the deficiency of adjustable central axes of these RCC devices also fail to facilitate insertion and mating maneuvers not advancing vertically downwards. In other words, these RCC devices cannot effectively accomplish insertion and mating maneuvers of asymmetrical (such as square) workpieces that require precise alignment, or insertion and mating maneuvers that advance in non-vertical directions.